Text 17

uttamah purushas tv anyah
paramatmety udahrtah
yo loka-trayam avisya
bibharty avyaya ishvarah 

Translation

Besides these two, there is the greatest living personality, the Supreme Soul, the imperishable Lord Himself, who has entered the three worlds and is maintaining them. 

Commentary by Srila Prabhupada

The idea of this verse is very nicely expressed in the Katha Upanishad (2.2.13) and Shvetasvatara Upanishad (6.13). It is clearly stated there that above the innumerable living entities, some of whom are conditioned and some of whom are liberated, there is the Supreme Personality, who is Paramatma. The Upanishadic verse runs as follows: nityo nityanam cetanas cetananam. The purport is that amongst all the living entities, both conditioned and liberated, there is one supreme living personality, the Supreme Personality of Godhead, who maintains them and gives them all the facility of enjoyment according to different work. That Supreme Personality of Godhead is situated in everyone’s heart as Paramatma. A wise man who can understand Him is eligible to at in perfect peace, not others.

Commentary by Sri Visvanatha Cakravarti Thakur

Having just spoken about the impersonal brahman, which the jnanis worship, the Lord now speaks about the paramatma which the yogis worship. The word tu indicates a distinction from what was previously spoken. As the yogi is a different worshipper than the jnani, the object worshipped will also be different.

The Lord shows the nature of paramatma. Paramatma is he who, though having the nature of commanding (isvara) and being unchanging (avyayah), enters into the three worlds completely and supports and protects it (bibharti).